Electrical signaling system



Se t. 28, 1937. 1 E. RYALL ELECTRICAL SVIGQNALING SYSTEM Filed Sept. 26, 1935 Iwvefii'or: leowarcl r1res2 H 322 AZ'Larney lent transmitted Patented Sept. 28, 1937 UNITED STATEIS 2,094,101; smcrmcsr. SIGNALING SYSTEM Leonard Ernest Ryall, Eastcote, Ruisllp, England Application September 26, 1935, Serial No. 42,331 In Great Britain September 26, 1934 12 Claims. (Cl. 179-18) The present invention concerns electrical signaling systems in which signals which may be speech or voice current signals or their equivain one channel or path are adapted to exert a controlling influence in their own or another path.

For instance in two-way complementary circuits for speech transmission it is desirable to arrange that the transmission of speech in one channel and in one direction should increase the attenuation of the channel through which speech passes in the opposite direction so as to eliminate echo effects. At the same time it is necessary that the attenuation should fall immediately speech has ceased to enable speech to be transmitted in the opposite direction. Now there are many circumstances in practice where the microphone or transmitter is located in a situation where it is subjected to a considerable amount of background noise and consequently such noise if in suflicient volume may act to prevent the attenuation of the channel through. which speech currents pass in. the opposite direction to the noise currents from being restored to permit such speech currents to pass or only if such speech currents are of a high value to enable the effect of the noise currents to be overcome.

Another application of the invention relates to radio telephone systems such as are employed in aeroplanes where noise is very heavy and where it is desirable to discriminate between speech and noise and thereby effect-a switching operation when speech is initiated to actually out out say a receiving circuit as long as the speech so initiated continues.

The object of the present invention therefore is to provide means whereby the harmful effect of such noise currents is reduced or eliminated, and according to the present invention this is effected by providing means capable of responding difierently to noise currents on the one hand and speech or signal currents on the other hand in dependence upon whether the currents in question are of a steady or fluctuating nature.

It has been found that a very large amount of background noise such as that which exists in a busy street, a workshop or a power house or in the vicinity of engines or-like machinery is substantially constant whereas all speech is of an intermittent character due to pauses between words and sentences and even in words themselves. I

In my previous British Patents Nos. 415,767 and 430,158, the control of the attenuation of one circuit is efiected by charging a condenser by rectified currents derived from signaling currents transmitted in the opposite direction and it is necessary for the condenser to dischargerapidly on the transmission in the latter direction ceasing to enable transmission to take place in the first circuit. As normally noise currents will have a similar effect to the signaling currents it will be clear that where these are of a serious character there is a danger of the condenser never being discharged, and two ways of obviating this danger will be described by way of example only, it being understood that the invention is in no way restricted to the particular arrangements described nor is it limited to the control of attenuation in a circuit because the condenser referred to might be connected in the grid circuit of a valve, having a relay in its anode circuit which is operated or not depending uporrthe potential applied to the grid. Obviously the relay could bring about any switching operation required.

In the drawing Fig. 1 indicates an arrangement by which the condenser, the voltage across which controls the attenuation, is arranged to be afiected only by the intermittent signaling or speech currents and not by the steadier noise currents, while Fig. 2 indicates an arrangement by which the different effects of the signaling and noise currents are employed to control the attenuation.

Referring to Fig. 1, currents derived from one circuit or channel are supplied to the primary winding of transformer Tl in the secondary circuit of which is connected a rectifier RI and a condenser Ci, so that the potential across the I condenser varies in accordance with the strength of the derived currents. A primary winding of a second transformer T2 is connected across the terminals of the condenser Cl, while to the secondary winding is connected a rectifier R2 and a condenser C2, the voltage across which determines either the attenuation of the network in the circuit or channel which requires to be controlled or the operation of a relay or like switching device while Rs represents the resistance which acts to discharge the condenser C2 but only if the charging of the condenser C2 should cease after an interval of time greater than that normally existing between words and syllables.

It will be clear that steady currents. i. e. noise currents of a steady nature derived from the first I circuit or channel, will cause thepotential across 'the condenser Ci to remain steady and consecurrents will have no efiect whatever on the voltage of the condenser C2. On the other hand irregular or intermittent. currents, such as signaling or speech. currents, will produce a potential across the condenser CI which will be continually varying. Hence the current through the primary of the transformer T2 will vary in accordance with these variations and these variations which are transmitted through the transformer will be rectified by R2 and in consequence a potential will be created across the terminals of the condenser C2.

Hence the noise currents will not affect the attenuation in- .the circuit to be controlled while the speech or signaling currents will. It will be understood that valves could be employed if necessary to amplify the fluctuations past thecondenser Cl.

Referring to Fig. 2 the currents derived from,

one circuit or channel are supplied to the primary of the transformer T3. This transformer has two secondary windings to one of which a rectification arrangement is connected comprising the rectifiers R3 and R4 and condensers C3 and C4,

arranged in known manner as shown to give full wave rectification. A resistance RS2 is connected across .the condensers C3 and C4 in series, the arrangement being such that the voltage across the two condensers in series controls the attenuation of the circuit to be controlled and'the resistance RS2 acts to discharge the condensers when the derived currents cease, the ratio of discharge time to charging time being large so that they remain charged during pauses between words, syllables and so forth. To the other winding a similar rectification arrangement is provided and across the terminal of the condensers C5 and C6 in addition to the resistance RS3 which effects the discharge with the variations of the derived currents, for instance within one fortieth of a second there is connected a rectifier R1 in series with a condenser Cl.- The rectifier R1 may be shunted by a high resistance if desired as shown. The condenser Cl is connected in series with the condensers C3 and C4 as shown so that any voltage across the condenser C! will affect the volt-age by which the attenuation or other operation is controlled. The arrangement is such that the condensers C3 and C4 charge rapidly and discharge relatively slowly, that is to say they only completely discharge after the derived currents have ceased for a period and are not discharged between words and syllables. Condensers C5 and C6 charge rapidly and discharge rapidly, that is to say, they discharge between syllables, signals or words and condenser C1 charges slowly and discharges rapidly, that is to say it discharges between syllables and words.

It will be noted that the rectifiers R5 and R6 are arranged in the opposite direction compared with the rectifiers R3 and R4 so that the potential across the condensers C5, C6 and C! will be in opposition to the voltage across the condensers C3 and C4. This will be seen from the following considerations. According to the usual convention, current fiows through a rectifier in the direction of the arrow head formed by the triangular portion of the symbol. Thus, considering the four rectifiers R3, R4, R5 and R6, it will be understood that if at any particular instant in one half-cycle current tends to flow through the rectifier R3, current will also tend to flow through the rectifier R6 but no current will flow through the rectifiers R4 and R5. During the nexthalf-cycle current will tend to fiow through units.

Consider now the case in which current tends to flow through the rectifiers R3.and R6. As

regards the rectifier R3, the circuit is as follows: secondary winding of transformer T3, positive pole to negative pole of rectifier R3, condenser C3 to the-secondary winding of transformer The upper plate of the condenser C3 will thus acquire a positive charge and the lower plate a negative charge. In a similar manner the upper plate of the condenser C6 will acquire a negative charge and the lower plate a positive charge.

During the next half-cycle current will tendv to flow through the rectifiers R4 and R5 and as regards the rectifier R4 the circuit extends as follows: secondary winding of transformer T3, condenser C4, positive pole to negative pole of rectifier R4 to the secondary winding of transformer T3. The upper plate of condenser C4 will thus acquire a positive charge and the lower plate a negative charge. Similarly the upper plate of condenser C5 will acquire a negative charge and the lower plate a positive charge.

It will be seen therefore that in two successive cycles the upper plates of condensers C3 and C4 will acquire a positive charge and the lower plates a negative charge while the upper plates of condensers C5 and C6 will acquire a negative charge and the lower plates a positive charge, that is to say, the voltage across condensers C3 is at all times in opposition to the voltage developed across condensers C5 and C6.

Further, since the condenser Cl is connected in parallel with condensers C5 and C6, a voltage will be developed across condenser C1 which will be in the same sense as that developed across condensers C5 and C6--that is, condenser C! will have a negative charge on the upper plate and a positive charge on the lower plate-and hence it will be in opposition to the voltage developed across condensers C3 and C4. The operation is as follows:

In the case of noise or steady derived currents the condensers C5 and C6 will become charged to a steady potential and also the condenser CI, but it will be clear that the time taken for the condenser C1 to reach the potential of the condensers C5 and C6 will depend upon the value of the resistance RS4 and the resistance of the rectifier R1 when current is flowing in the high res stance direction and this charge current is long compared with the duration of a speech syllable or signal.

The potential across the condenser C1 being in opposition to the potentials across the condensers C3 and C4, the effect of noise currents can be balanced out as regards the attenuation of the circuit which is to be controlled. On the other hand if the derived currents are variable as in the case of speech or signaling currents, and as speech and signaling current superimposed on the noise current must result in a current of greater amplitude than the background noise currents, the potential across the condensers C3 and C4 will fluctuate in dependence upon the amplitude of the signals, while the potential across the condenser C1 will remain at a value dependent upon the amplitude of the background noise. This is because increases of potential across the condensers C5 and 06 can only be transmitted slowly to the condenser Cl. On the other hand decreases of potential across the condensers Cl and C4 and C6 result in a very rapid fall in the potential across the condenser C! so that every interruption in the speech or signaling currents has the effect of counteracting any slight increase of potential which might have reached Cl due to a comparatively prolonged high amplitude component of the speech or signaling currents and is immediately lost when the first interruption occurs.

A useful application of the invention is to radio telephone transmission between aeroplanes. Here it is desirable that normally the receiving currents should be in action and cut out when the associated transmitter is in use. Dueto the heavy noises whichexist manual control means have hitherto been considered essential but according to the invention it is possible to arrange for the transfer to be controlled by the airman speaking. The. discriminating arrangements of the invention enable speech to produce an effect which is not produced by noise and so effect the operation of a relay orlike switching device to do what has hitherto been done manually.

It will be understood that the invention is not confined to the particular examples described and considerable departure may be made in the circuit details without departing from the spirit of the invention as set out in the opening paragraphs.

I claim:

1. In combination in an electrical signaling system for transmitting speech currents, at line over which speech and noise currents pass, a circuit electrically associated with said line, a condenser included in said circuit, a rectifier included in said circuit to convert the speech and noise currents into direct current and thereby determine the charge on said condenser, slow-operating means for discharging said condenser, a second circuit electrically associated with such line, a condenser included in said second circuit, a rectifier included in said second circuit to convert the speech and noise currents into direct current and thereby determine the charge on said second condenser, delaying means to cause said second condenser to charge slowly and one-way means acting to permit said second condenser to discharge quickly, connecting means to enable the charges on said two condensers to act in opposition to each other, and a second line to which the potential which is derived from said condensers is applied for control purposes when the steady noise currents are supplemented by the irregular speech currents.

2. In combination in an electrical signaling system for transmitting speech currents, a line over which speech and noise currents pass, a circuit electrically associated with said line, a condenser included in said circuit, a rectifier included in said circuit to convert the speech and noise currents into direct currents which are applied directly to said condenser, slow-operating means for discharging said condenser, a second circuit electrically associated with said line, a condenser included in said second circuit, a rectifier included in said second circuit to convert the speech and noise currents into direct currents and thereby determine the charge on said second condenser, delaying means to cause said second condenser to charge slowly, connecting means to enable the charges on said two condensers to act in opposition to each other, and a second line to which the potential which.is derived from said condensers is applied for control purposes when the steady noise currents are supplemented by the irregular speech currents.

3. In combination in an electrical signaling system for transmitting speech currents, at line' over which speech and noise currents pass, a circuit electrically associated with said line, a condenser included in said circuit, a rectifier included in said circuit to convert the speech and noise currents into direct currents which are applied denser, one-way means to cause said second condenser to discharge quickly, connecting means to enable the charges on said two condensers to act in opposition to each other, and a second line to which the potential which is derived from said condensers is applied for control purposes when the steady noise currents are supplemented by the irregular speech currents.

4. In combination in an electrical signaling system for transmitting speech currents, a line over which speech and noise currents pass, a first circuit electrically associated with said line, a second circuit electrically associated with said line, a condenser in each of said circuits, a rectifier included in each of said circuits for converting the speech and noise currents into direct currents and thereby determine the charge on each of said condensers, electrical connecting means to enable said two condensers to act in opposition, and delaying means to cause one of said' condensers to charge slowly whereby a resultant direct current potential is obtained across said two condensers depending solely on the potential fluctuations of the speech currents.

5. In combination in an electrical signaling system for transmitting speech currents, a line over which speech and noise currents pass, two circuits each including a dry plate rectifier and a condenser, means for electrically associating one of said circuits with said line, and electrical connecting means for said circuits to give a resultant direct current potential across said condensers depending upon the irregularities produced by the speech currents when superimposed upon steady noise currents.

6. In combination in an electrical signaling system for transmitting speech currents, a line over which speech and noise currents pass, a network comprising at least two circuits electrically associated with said line, a plurality of dry plate rectifiers in said network for converting the speech and noise currents into direct currents, condensers in said network, and leads extending from points in said network between which a voltage is obtained which depends only on said speech currents.

7.,In combination in an electrical signaling system for the transmission of speech currents, a line over which speech and noise currents pass, a circuit electrically associated with said line, a second circuit, a transformer having a primary winding in said first circuit and a secondary winding in said second circuit, a dry-plate rectifier in said first circuit for converting the speech and noise currents into direct currents whereby a steady potential is applied across said primary winding due to noise currents and a fluctuating potential due to speech currents is transferred to said secondary winding, a condenser in said second circuit the charge on which is dependent on the speech currents only, and a second line to which the potentials derived from said condenser are applied for control purposes when the steady noise currents are supplemented by the fluctuating speech currents.

8. In combination in an electrical signaling system for transmitting speech currents, a line over which speech and noise currents pass,\,a circuit electrically associated with said line, a rectifier included in said circuit to convert the speech and noise currents into direct currents, a condenser in said circuit to which the direct currents are' directly applied, slow-operating means for discharging said condenser, a second circuit electrically associated with said line, a condenser included in said second circuit, a rectifier included in said second circuit to convert the speech and noise currents into direct currents and thereby determine the charge on said second condenser, delaying means to cause said second condenser to charge slowly and one-way means acting to permit said second condenser to discharge quickly, connecting means to enable the charges on said two condensers to act in opposition to each other, and a second line to which the potential which is derived from said condensers is applied for control purposes when the steady noise currents are supplemented by the irregular speech currents.

9. In combination in an electrical signaling system for transmitting speech currents, a line over which speech and noise currents pass, a circuit electrically associated with said line, a rectifier included in said circuit to convert the speech and noise currents into direct currents, a condenser in said circuit to which the directlcurrents are directly applied, a second circuit electrically associated with said line, a rectifier included in said second circuit to convert the speech and noise currents into direct currents, a second condenser in said second circuit to which said direct currents are directly applied, a third condenser in said second circuit electrically associated with said second condenser, delaying means to cause said third condenser to charge slowly and oneway means acting to permit said third condenser to discharge quickly, connecting means to enable the charges on said first and third condensers to act in opposition to each other, and a second line to which the potential which is derived from said first and third condensers is applied for control purposes when the steady noise currents are supplemented by the irregular speech currents.

10. In combination in'an electrical signaling system for the transmission of speech currents, a line over which speech and noise currents pass, a circuit electrically associated with said line, a second circuit, a transformer having a primary winding in said first circuit and a secondary winding in said second circuit, a dry-plate rectifier in said first circuit for converting the speech and noise currents into direct currents, means in said first circuit for causing a steady potential to be applied across said primary winding due to the rectified noise currents and permitting a fiuctuating potential due to the rectified speech currents to be transferred to said secondary winding, a-condenser in said second circuit the charge on which is dependent on the speech currents only, and a second line to which the potential derived from said condenser is applied for control purposes when the steady noise currents are supplemented by the fluctuating speech currents.

11. In combination in an electrical signaling system for the transmission of speech currents, a line over which speech and noise currents pass, a circuit electrically associated with said line, a second circuit, a transformer having a primary winding in said first circuit and a secondary winding in said second circuit, a dry-plate rectifier in said first circuit for converting the speech and noise currents into direct currents, a condenser connected across the primary winding of said transformer whereby a steady potential is applied across said primary winding due to rectified noise currents and a fluctuating potential due to rectified speech currents is transferred to said secondary winding, a condenser in said second circuit the charge on which is dependent on the speech currents only, and a second line to which the potentials derived from said condenser are applied for control purposes when the steady noise currents are supplemented by the fluctuating speech currents. I

12. In combination in an electrical signaling system for the transmission of speech currents, a line over which speech and noise currents pass, a circuit electrically associated with said line, a second circuit, a transformer having a primary winding in said first" circuit and a secondary winding in said second circuit, means associated with said first circuit for causing a steady potential to be applied across said primary winding due to noise currents and permitting a fluctuating potential due to speech currents to be transferred to said secondary winding, a dry-plate rectifier in said second circuit for rectifying the current variations due to the speech currents, a condenser in said second circuit the charge on which is dependent on the speech currents only, slow-discharging means connected across said condenser, and a second line also connected across said condenser for eilecting a control when the steady noise currents are supplemented by the fluctuating speech currents.

LEONARD ERNEST RYALL. 

